Solar cells are well known devices that have been developed over a long period of time. For example, FIG. 1 illustrates a liquid junction based dye-sensitized solar cell (DSSC) generated by Michael Grätzel that offers the advantage of high efficiency, manufacturability, and low cost. According to the literature, an efficiency of 11.1% has recently been achieved with such a cell. A typical DSSC cell is composed of a transparent anode made of fluorine-doped tin oxide deposited on a glass substrate, a porous layer of titanium dioxide nanoparticles coated with an absorbing dye (i.e. ruthenium-polypyridine), a metallic cathode, and an electrolyte solution containing a redox couple (e.g., I−/I3−) as shown in FIG. 1. These components are relatively simple to assemble and inexpensive compared to silicon based solar cells. The principle of operation of the DSSC is significantly different from that of conventional semiconductor solar cells in which the semiconductor is the source of the photo generated electron/hole pairs and also provides the potential barrier that separates these charges resulting in a photocurrent. In contrast, in the DSSC, the semiconductor is used solely for charge separation and the electron/hole pairs are generated in a separate photosensitive dye attached to the semiconductor. As shown in FIG. 1, the Grätzel solar cell consists of a TiO2 layer forming a nanoporous structure with a dye (e.g., ruthenium-polypyridine) spread throughout its surface. The dye molecules are small and in order to capture a reasonable amount of the incoming light the nanoporous structure is used as a scaffold holding large numbers of the molecules in a 3D matrix, vastly increasing the number of molecules for a given surface area. The charge separation is provided by the semiconductor-liquid junction contact. The TiO2 layer sits on a transparent anode made of fluorine-doped tin oxide (SnO2:F) deposited on the side of the glass plate facing the TiO2 layer.
The electrolyte solution also holds a redox couple (e.g., I−/I3−) in the space between the dye coated TiO2 and a cathode, typically a thin film of platinum metal. Photons enter the cell through the transparent SnO2:F window, and, if they have enough energy, they are absorbed by the dye creating an excited dye state with the photoelectron in a higher energy level and a hole left behind in a lower energy state. From this excited state an electron is “injected” into the conduction band of the TiO2. This way the dye molecule is oxidized and would decompose if the hole in the lower energy state didn't quickly react with iodide in the electrolyte oxidizing it to form triiodide (dye regeneration reaction): 3I−−2e−→I3−
The reaction with iodide occurs very quickly compared to the recombination of the injected electron with the oxidized dye molecule, preventing effectively short-circuiting the solar cell. The injected electron then travels to the cathode via the external circuit and the triiodide recovers its missing electron by diffusing through the solution to the cathode where it is reduced back to iodide (redox regeneration reaction): I3−+2e−→3I−.
Another existing solar cell technology developed by Texas Instrument is shown in FIG. 2. In this approach, electrons and holes are generated in solid junctions inside spherical silicon particles coated with catalytic metals that are in contact with a HBr-containing solution. The reaction of the electrons leads to hydrogen [Redox system 1 (=H+/H2)] and the reaction of the holes leads to bromine [Redox system 2 (=Br−/Br2)] and these reaction products are physically separated and coupled to electrodes in a hydrogen/bromide fuel cell. Electrical energy is generated when hydrogen and bromine are allowed to react in the fuel cell and the products of the fuel cell reaction, hydrogen and bromine ions, are brought back to the photoactive cell where they are used again as electrons and holes carriers.
It is desirable to provide a nano power cell that separates the two photo-generated redox pairs while providing a nano power cell and it is to this end that the disclosure is directed.